The present invention relates to a nonvolatile memory array, and particularly to an array of nonvolatile memory cells having switchable resistor memory elements.
There are materials that have at least two distinct stable resistivity states. This class of materials can be switched from a high-resistivity state to a low-resistivity state by applying a voltage across the material having a given polarity. To switch the material from the low-resistivity state back to a high-resistivity state, a voltage having the opposite polarity can be applied.
Some of these materials can be switched between resistivity states at relatively low applied voltages, for example two volts or less. These properties would make these materials attractive for use in nonvolatile memory arrays, which retain their memory state even when power is removed from the device. Low-voltage switching is advantageous to reduce power consumption in devices, but many challenges must be overcome to provide the low voltages and reversible voltages required to operate cells incorporating such material, and to avoid accidental programming and/or erase during read.